From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F001E317145; Thu, 11 Jun 2026 16:48:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781196518; cv=none; b=RbuwpTSIWZo5cbA57IKuWurp9k3y6HILyYGVgA9iwGcReNRrihazK432B/CZGCdgNvxKpqAgy/rXHzFHO9p5rzmVT4h3BrOi/lcCGaspStuxSRLg/njf+RvxmEmxUJNnRUVcTixfQ3qOxrW0UczeUjb2qwJQq2616jP8pa1FJwk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781196518; c=relaxed/simple; bh=rBJ9afOA/bVjFNjhNE0EjYjuArt/4EBnlHJ19qvrP7c=; h=Date:To:From:Subject:Message-Id; b=mpuVV9kNVhFXGGouPh4X0JYCC5Cje81eL8i3MbqX1NPI9bVhmjb95ymSeqDx9fN/uDBqpioIZf5xAEDbyuvzsS0TCLw6y6whI9aRFbM0Dq9Club98RfX8ZcJOoQDy3wwZvacoX6GGVl6b+I8LI3nMyhEFq7xgzXMPY6JkwYk6K0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=l5Y6gYkp; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="l5Y6gYkp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6F6C71F00893; Thu, 11 Jun 2026 16:48:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1781196516; bh=CDA8w4OtKvS5XoTW+gbDG90BRFfFcRfr3ZoME+3PPpw=; h=Date:To:From:Subject; b=l5Y6gYkpPKgNq+9b70QQvtP6gzRuFiYQWXTd/cNrvShwSBYlBVL1Rh5L3wEBNsq9b Pll5LPDq/vjLqyZrMReI14RurmllmeFsohqiUaNbFCeC+rdpEImN9h7mYKScCniTPQ G8TS0yOI3gJTv2nqLa62I56/PiwI3V69tdUuTLDs= Date: Thu, 11 Jun 2026 09:48:36 -0700 To: mm-commits@vger.kernel.org,zenghui.yu@linux.dev,stable@vger.kernel.org,sj@kernel.org,roman.gushchin@linux.dev,qi.zheng@linux.dev,nphamcs@gmail.com,muchun.song@linux.dev,david@fromorbit.com,shakeel.butt@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-shrinker-do-not-hold-rcu-lock-in-shrinker_debugfs_count_show.patch added to mm-unstable branch Message-Id: <20260611164836.6F6C71F00893@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/shrinker: do not hold RCU lock in shrinker_debugfs_count_show() has been added to the -mm mm-unstable branch. Its filename is mm-shrinker-do-not-hold-rcu-lock-in-shrinker_debugfs_count_show.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-shrinker-do-not-hold-rcu-lock-in-shrinker_debugfs_count_show.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Shakeel Butt Subject: mm/shrinker: do not hold RCU lock in shrinker_debugfs_count_show() Date: Wed, 10 Jun 2026 16:20:48 -0700 Reading the debugfs "count" file of a memcg-aware shrinker can sleep inside an RCU read-side critical section: BUG: sleeping function called from invalid context at kernel/cgroup/rstat.c:421 RCU nest depth: 1, expected: 0 css_rstat_flush mem_cgroup_flush_stats zswap_shrinker_count shrinker_debugfs_count_show shrinker_debugfs_count_show() invokes the ->count_objects() callback under rcu_read_lock(). The zswap callback flushes memcg stats via css_rstat_flush(), which may sleep, so it must not run under RCU. The RCU lock is not needed here. mem_cgroup_iter() takes RCU internally and returns a memcg holding a css reference (dropped on the next iteration or by mem_cgroup_iter_break()), so the memcg stays alive without it. The shrinker is kept alive by the open debugfs file: shrinker_free() removes the debugfs entries via debugfs_remove_recursive(), which waits for in-flight readers to drain, before call_rcu(..., shrinker_free_rcu_cb). The sibling "scan" handler already invokes the sleeping ->scan_objects() callback with no RCU section. Drop the rcu_read_lock()/rcu_read_unlock(). Link: https://lore.kernel.org/20260610232048.62930-1-shakeel.butt@linux.dev Fixes: 5035ebc644ae ("mm: shrinkers: introduce debugfs interface for memory shrinkers") Signed-off-by: Shakeel Butt Reported-by: Zenghui Yu Closes: https://lore.kernel.org/all/c052a064-cddb-494f-a0d8-f8a10b4b1c4d@linux.dev/ Suggested-by: Nhat Pham Reviewed-by: SeongJae Park Reviewed-by: Qi Zheng Tested-by: Zenghui Yu (Huawei) Reviewed-by: Nhat Pham Cc: Dave Chinner Cc: Muchun Song Cc: Roman Gushchin Cc: Signed-off-by: Andrew Morton --- mm/shrinker_debug.c | 4 ---- 1 file changed, 4 deletions(-) --- a/mm/shrinker_debug.c~mm-shrinker-do-not-hold-rcu-lock-in-shrinker_debugfs_count_show +++ a/mm/shrinker_debug.c @@ -57,8 +57,6 @@ static int shrinker_debugfs_count_show(s if (!count_per_node) return -ENOMEM; - rcu_read_lock(); - memcg_aware = shrinker->flags & SHRINKER_MEMCG_AWARE; memcg = mem_cgroup_iter(NULL, NULL, NULL); @@ -88,8 +86,6 @@ static int shrinker_debugfs_count_show(s } } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL); - rcu_read_unlock(); - kfree(count_per_node); return ret; } _ Patches currently in -mm which might be from shakeel.butt@linux.dev are mm-shrinker-do-not-hold-rcu-lock-in-shrinker_debugfs_count_show.patch